Once the condenser water has been adjusted to get the optimum compressor discharge pressure, look at the liquid line sight glass. At this setting, the glass should show a solid stream of refrigerant with no bubbles. The glass should be clear. Bubbles in the liquid line sight glass show the chiller isn't getting a full supply of refrigerant. The bubbles are not air, they are refrigerant vapor. This means the chiller isn't working at full efficiency, and suction pressure will be low. The cause might be discharge pressure too low, and tweaking the condenser discharge pressure a few pounds might clear up the sight glass. Or the cause may be a short refrigerant charge, in which case the leak needs to be found and fixes as soon as possible, before adding more refrigerant.